Hydraulic Mining System for Tabular Orebodies Utilising Directional Drilling

ABSTRACT

A mining system for extracting ore using directional chilling techniques to obtain access to the orebody. Spaced-apart roadways are formed in the ore formation, with a downhill roadway being lower in elevation than the other roadway, and the downhill roadway having a ditch therein draining downhill. A borehole is formed between roadways in the ore formation using the directional drill bit, and then the end of the drill string is equipped with a jetting nozzle. The jetting nozzle is moved within the borehole to erode the formation and mine the ore. In one embodiment, a slurry of mined ore and jetting fluid flows as a slurry down the intersection of the mined face and the floor towards a ditch formed in the downhill roadway. In another embodiment, a slurry of the mined ore and the jetting fluid flows down the borehole, and then down the ditch formed in the downhill roadway. In each case, the ore flows down the downhill roadway to a sump. From the sump, the ore is carried to the surface for transportation and eventual refining or use.

RELATED PATENT APPLICATIONS

This PCT application claims the further benefit of Australianprovisional application 2010903253 filed on 21 Jul. 2010, and Australianprovisional application 2011900008 filed on 1 Jan. 2011.

BACKGROUND OF THE INVENTION

The production of many goods for commercial and private use requires theutilisation of numerous types of minerals, or orebodies, and theprocessing of the same from raw materials into finished goods.Similarly, the production of much of the heat and electrical energy inuse today requires a substantial amount of coal. The minerals utilisedin industry are obtained from the crust of the earth, usually by miningthe same. Before mining machines were in general use, the mining ofminerals was carried out manually by using picks and shovels, as well aswagons pulled by horses or mules. In order to increase the productionlevel of minerals, mining machines were invented to allow the mineralsto be more easily mined from the earth and transported to the refiningand manufacturing sites.

Minerals are mined by different methods depending on where the mineralsare found in the crust of the earth. When the minerals are found nearthe surface of the earth, the overburden is first removed and then theminerals are mined by surface equipment, such as power shovels,bulldozers, drag lines, etc. Minerals are also located underground tothe extent that the mining thereof must be carried out by tunneling intothe earth to extract the minerals. Numerous types of underground miningtechniques have been developed to efficiently and safely recover theminerals.

The underground mining of tabular orebodies, and in particular coal ortrona, generally involves the use of mining equipment which cutsroadways in the orebody. In one form of underground mining, a series ofpillars are formed so that a portion of the ore is removed and a portionof the ore (the pillar) is left in place. The pillars support the roofof the mine and prevent it from caving in and filling the mine workings.This is referred to as either “bord and pillar” mining or “room andpillar” mining. Sometimes the pillars of ore are removed on retreat fromthe mine to extract the remaining pillars of ore. The removal of thepillars causes the roof to cave in and form a goaf or gob. In additionto this technique of underground mining, a more productive systeminvolves extracting the ore using longwall mining techniques.

The longwall mining systems essentially divide the entire coal seam intoa number of “panels” which are typically 3 to 4 km deep or long, 200 to350 m wide and 1.5 to 5 m high. Roadways are initially excavated on eachside of each panel to provide transportation of equipment, miners andallow transport of the mined coal during mining of the panel. Oneroadway is a main gate and the other roadway is a tail gate. The maze ofroadways in a coal seam can be used to ventilate the working area andremove dangerous gases, such as methane and carbon dioxide, and providefresh air.

A large and heavy mining machine is equipped with a rotating shearerwhich is moved laterally back and forth across the face of the panel tosuccessively remove thick sheets or slices of coal. Because of thecomplexity and size of such mining machines, they are extremelyexpensive. The slice of coal removed during a single pass can be about Im thick. The chunks of coal which are removed from the face of the panelfall into an armoured face conveyor which moves the chunks of coallaterally to the main gate. At the main gate or roadway, the coal can bepulverised into smaller pieces and loaded onto a long conveyor to betransported along the main gate and eventually to the surface.

The longwall mining machine further includes a number of hydraulic jackswhich extend across the width of the panel and function to support theroof of the mined area just in back of the face of the coal panel. Thehydraulic support jacks move with the mining machine forwardly as therotating shearer is moved forward to extract coal from the face of thepanel. Once the mining machine moves forwardly during the miningoperation, the portion of the roof that is no longer supported by thehydraulic support jacks caves in and forms a goaf. Each panel of coal ismined in the manner described until the entire coal seam is spent. Thelongwall mining system can either operate as advancing longwalls, or asretreating longwalls, depending on whether the gateroads are progressedwith the face of the panel, or the face is retreated between theroadways. In either case, a goaf is formed between the gateroads in thewaste zone of the mined area.

Where appropriate, hydraulic jet mining is used to recover ore fromsurface deposits or from underground deposits. The hydraulic miningsystem is particularly suited to the underground environment where theore is weak and the roof and floor rocks are hard to provide support andguard against cave in of the roof. It is also a suitable method to usewhere the orebody is tabular and located on a slope. As the ore ismanually eroded by the hydraulic jet, it is carried downwardly with theassistance of gravity along the slope of the mine floor. Hydraulic jetmining is generally accomplished by using high volumes of pressurisedwater projected at the orebody from a nozzle or monitor which iscontrolled by an operator. Limitations of hydraulic jet mining includethe effective dispersal range of the jet, which is approximately 30 m,and the limited visibility afforded to the operators. Typical examplesof such mining systems were Sunagawa Colliery in Japan, and theStrongman Mine in New Zealand.

Directional drilling has been in use for some time in the petroleumindustry, and in coal mining where it is used for either gas drainageoperations or for exploration. In its preferred form, directionaldrilling involves the use of a bottom hole assembly consisting of adownhole mud motor with a bent sub which drives a rotary drill bit. Thedrilling of the borehole is guided by the use of a survey system whichdetermines the orientation of the borehole, as well as the toolfaceangle of the bent sub. Based on information from the survey system, theoperator may rotate the drill string to re-orient the bent sub and thussteer the borehole in another direction. In addition to downhole motors,alternative bottom hole assemblies may be used for directional drilling.The use of offset jets has long permitted the direction of a borehole tobe corrected. The process used is similar to that used for a downholemotor and bit, except the corrected borehole is drilled by high pressurejets. Other directional control systems are also used in drilling. Thesemay involve a rotating drill string with a bottom hole assemblyconsisting of pressure pads which push the bit to one side of theborehole, or the other, so that a desired borehole path is followed.

SUMMARY OF THE INVENTION

In view of the foregoing, it can be seen that a need exists for a methodof mining underground orebodies, where the equipment is much lessexpensive and complicated, as compared to the longwall mining technique.The various features of the invention combine both the practise ofdirectional drilling and hydraulic mining to extract a sloping tabularore body in an underground environment. In its preferred embodiment,roadways are driven or formed underground to permit ventilation andaccess in the normal manner. Gateroads are formed with a dip, and withrespective ditches therein to provide downhill drainage of the minedslurry of ore and jetting water. The ditch in the downhill gateroadpermits the transport of the slurry of the jetting fluid and ore down toa sump, from whence the slurry can be pumped to the surface.Alternatively, the ore may be separated from the fluid at the sump andtransported to surface. Drilling is used to connect gateroads on eachside of an ore panel with a borehole. Drilling is normally of adirectional nature and orientated off of the dip direction of the orebody. Directional drilling between the gateroads may be achieved usingdownhole mud motors, water jets or other systems to provide directionalcontrol of the borehole formation. Such systems typically utilise a formof borehole survey system.

On reaching the opposite gateroad, the directional bottom hole assemblyis exchanged for a jetting bit which erodes the formation laterally.This is done either physically by changing the bit, or by remotelychanging the mode in which the bit operates, such as a method of pumpinga sealing ball down the drill string and pressurising it until apressure relief port blows, thus creating a lateral jet. In any event,the hydraulic jet at the end of the drill string is directed to thesidewall of the borehole adjacent to the goaf area to erode the ore,while moving along the borehole. The ore is thus effectively mined fromthe borehole between the roadways, except for the formation of a pillar,if desired. It can be appreciated that the initial borehole is formed ata location where the mining of the panel is to be commenced.

The bulk of mining is achieved through the mechanism of erosion broughtabout by pumping a pressurised fluid from a lateral jet. The jet iscontrolled in order to drill in the direction of the orebody on thewaste or goat side of the face of the orebody. If the mode of operationis that the borehole is drilled updip, fluid and ore flow downhill andback towards the borehole along the solid bottom edge of the orebody.Where the borehole is essentially drilled down dip, the slurry of fluidand ore proceed down the intersection of the solid edge of the panelface with the floor of the orebody to the roadway at the lower level ofthe panel being mined, from thence flowing to the sump.

Where the borehole is drilled essentially up dip, the borehole must beof a sufficiently large diameter to permit the fluid and ore to passback through the borehole while the drill string is still in theborehole. A useful method to enlarge the borehole and remain in linewith the mining system is to use a fluid jet to erode the borehole andenlarge the diameter thereof. After the enlargement of the drilledborehole, the lateral jet bit is used to mine the ore. Where theborehole is drilled up dip, the preferred sequence is to drill theborehole from one roadway to the other roadway, ream it out, re-enterthe borehole with a jetting bit which will erode laterally, and thenmine on the waste side of the panel face with the ore and fluid passingdown the borehole to the lower roadway and thence to the sump. Dependingon the pressure of the fluid used with the hydraulic jet, it is possibleto mine the face of the ore panel with a height greater than thevertical diameter of the initial borehole.

Once a first pass of the mining operation is accomplished through thefirst borehole, a second borehole is formed downhill and parallel to thefirst borehole. A subsequent mining pass is accomplished using thesecond borehole to erode a further layer of ore from the formation.Subsequent boreholes arc formed to allow additional mining passes todeplete the panel of ore located between the roadways.

It can be appreciated that rather than using expensive and extremelyheavy machinery for longwall mining, essentially the same result can beaccomplished using directional drilling to sequentially form boreholesbetween roadways, and then use a high pressure jet which traverses eachborehole to erode the ore panel. The mining of the ore continues in eachborehole until the panel is spent. According to this technique, theequipment can be easily moved from one ore panel to another in a shortperiod of time, thereby making the technique very cost effective. Thenature of the equipment means that it can be easily retrieved should acollapse of the borehole or face occur. Another borehole may then bedrilled and the mining process is recommenced through erosion. In theevent that the drill string is lost then its cost is small compared tothat of conventional longwall equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages will become apparent from the followingand more particular description of the preferred and other embodimentsof the invention, as illustrated in the accompanying drawings in whichlike reference characters generally refer to the same parts, functionsor elements throughout the views, and in which:

FIG. 1 shows a plan view of a panel being mined. The dip of the orebodyis down the page. The boreholes are drilled down dip along the line 2-2and the jetted face is along the line 3-3;

FIG. 2 shows a sectional view, taken along the line 2-2 of FIG. 1,through a panel where the boreholes are drilled down dip and extractionis taking place;

FIG. 3 shows a sectional view through a panel where the boreholes aredrilled up dip and extraction is taking place;

FIG. 4 shows a section taken along 4-4 of FIG. 1, through the miningzone; and

FIG. 5 shows a plan view of a panel being mined with boreholes which aredrilled up dip.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a plan view of a mineral panel that is being mined bydrilling down dip. The mining operation of the panel proceeds in thedrawing of FIG. 1 to the right, with the goaf (2) to the left and theunmined orebody (3) to the right. The angle or dip of the panel of orebeing mined is shown in FIG. 2, where the gateroad (10) is lower inelevation than the gateroad (5). The panel of ore of interest includesthe solid deposit of ore (3) to be mined, as well as the goaf (2) thathas been mined. The dip direction is marked by an arrow (18) in FIG. 1.illustrated also is a neighbour goaf (1) that was formed in the area ofthe previously mined neighbour panel. The neighbour goaf (1) isseparated from the current mining panel, i.e. solid ore (3) andassociated goaf (2), by gateroads (4, 5). On the lower side of the panel(2, 3) undergoing the mining operation are the lower elevation gateroads(10, 11). The gateroads (4, 5, 10, 11) slope downhill to the right ofthe figure and include respective ditches (not shown) to drain theslurry of ore and water down to a sump (12).

The gateroads (4, 5, 10, 11) are connected to main roadways (7, 8, 9)which are used for access and ventilation during development of themine. The sump (12) collects the slurry of ore and fluid. Drilling ofthe borehole (17) is initiated at the gateroad (5) at (19). The boreholeis shown as (17) and is drilled to gateroad (10) at (13). The borehole(17) can be drilled with diameters between about 0.1 m and 0.3 m, andpreferably about 0.15 m. The length of the borehole (17) is about thesame as the distance between opposite roadways, namely about 300 m. Thisdistance is to a significant extent controlled by ventilation needs. Theangle or dip of the borehole (17) with respect to a horizontal referencecan be anywhere between about 6 degrees and 45 degrees. It is noted thatthese dimensions and numerical limitations are not critical to theoperability of the methods of the invention. In any event, whiledrilling the borehole (17), the ore removed is also mined and recoveredby way of a slurry at the sump (12).

At the terminal location (13) of the drilled borehole (17), thedirectional drill bit is changed to a lateral jetting device (not shown)and the zone to the left of the borehole (17) is eroded. The goaf (2) isthereby formed. In the figure, the eroding bit is at (16) and a panelface (15) is formed which is advanced up dip. The eroded ore and fluidflow down the lower face (14) to downhill gateroad (10) into a ditch (23in FIG. 2), and thence down the ditch (23 in FIG. 2) to the sump (12).Once the ore has been mined from the initial borehole (17), the drillpipes are removed and the drilling equipment is moved downhill a shortdistance to drill a subsequent borehole where another mining operationis again carried out using the jetting nozzle. Depending on the roofbehaviour, it may be possible to erode all the ore from the eroding bit(16) to the goaf edge. If, however, roof control becomes an issue and itis not possible to erode back to the goaf edge, the preferable approachis to leave a pillar parallel to the borehole (17) to provide roofsupport. This pillar can be designed to crush as the goaf (2) fullyforms, or to remain standing.

The ore is transported to surface from the sump (12) either as a pumpedslurry or is separated at (12) and is carried to surface by such adevice as a conveyor while the water is pumped separately.

A pillar (6) is formed because the eroding jet is controlled so as notto erode the formation all the way to the roadway (5). The pillar (6) isConned adjacent to the gateroad (5) where the directional drillingequipment is located.

In another embodiment of the invention, it is possible to pre-drill allof the boreholes (17) in the panel and use them for drainage of waterand/or gas prior to mining.

FIG. 2 illustrates a borehole cross-section through the panel of FIG. 1.Up dip, the roadway (4) has a goat zone (1) uphill from it and istherefore damaged. Drilling of the borehole (17) in this embodimentbegins at the higher elevation roadway (5), and proceeds down to thelower elevation roadway (10). As noted above, at borehole location (13),a laterally eroding jet bit (not shown) is attached to the drill string(not shown) in the borehole (17). The jetting bit is shown at location(16) having eroded the zone (26). The shaded area (6) near roadway (5)depicts the pillar zone where mining does not take place so as topreserve the roadway (5) and the drilling machinery (27) locatedtherein. The drill pipe in the borehole (17) is pulled back by the drill(27) which is used to manipulate the orientation of the drill string inthe borehole (17) and with it the jetting bit. The roof above theorebody is marked as (21) and the floor as (20). Drainage ditches areformed in the floor of the roadways at (23, 24, 25). The ditch (23)carries the slurry of fluid and ore away from the mining area asoriginally did the up dip ditch (25) for the previously mined up dippanel. The ditch (24) carries drill fluid away from the directionaldrilling operation. The borehole spacing might be typically 5 to 10 m,limited by the eroding capability of the jetting bit within theparticular ore type. While not shown, the borehole (17) is drilled atdesired locations between roadways (5, 10) using directional and/orspatial sensors and other equipment well known in the art. A survey andmapping of the formation can be made to determine where the variousroadways should be made before the mining operation is commenced. Theactual mining operation can be carried out using a camera or othervisualisation device such as an acoustic scanner located at the jettingnozzle so that the operation can be observed and controlled by anoperator at a remote location. Cameras utilising self cleaning lensescan be used to provide an unobstructed view of the mining operation andthe need for adjustment thereof. Using a joystick, the operator cancontrol the orientation of the jetting nozzle to selectively erode theore panel, and at the same time remotely view the jetting operation toverify that it is progressing as desired. At times, if the drainage ofthe slurry is slowed due to blockage by excessive ore on the mine floor,borehole or ditches, the jetting erosion can be temporarily suspended sothat the additional fluid can be used to flood the area and clear thedrainage way of the excess ore. The advantage of the remote control ofthe jetting operation is that workers arc not in the area where there isa risk of the mine roof collapsing, or being overcome by dangerousgasses or outbursts.

FIG. 3 illustrates another embodiment showing a sectional view throughan ore panel where the borehole (17) has been drilled up dip fromroadway (10) to roadway (5). The borehole (17) has then been reamed to alarge size. The drill string (not shown) equipped with a jetting nozzlehas then been re-inserted into the borehole (17). The eroding jet bit isshown at location (33), and is moving downhill toward the roadway (10).The zone up dip of the eroding bit at (33) and below the roadway (5) hasbeen removed by the action of fluid erosion. The ore and fluid mined haspassed back down the enlarged borehole (17) to the drainage ditch (23).The zone (30) is not mined so as to form a barrier pillar and preventcaving damage to roadway (10). In its preferred embodiment, the enlargedborehole (17) is eroded to a larger size than the original borehole (17)by the use of a combination of different eroding bits, water flow oreroding time duration to suit requirements. The reaming of borehole (17)may also be accomplished by other means such as rotating mechanicalreamers.

FIG. 4 is an enlarged view of the mining face at section 4-4 of theoperation depicted in

FIG. 1. Here, the lateral jetting bit is at (16) in borehole (17). Thejetting bit (16) has lateral port(s) in it which make it jet laterallyfrom the bit (16). The jets which issue from the lateral port(s) may bedirected to sweep at different orientations by twisting the drill stringwithin the borehole (17) using the drilling machine. This twisting iscontrolled by the operator working under the guidance of the surveysystem and visualisation system contained within the drill string anddelivering information to the operator.

The roof of the orebody is shown at (21) and the floor at (20). The facewhich has been eroded is at (15) and solid ore is to the right of thejetting bit (16) and between the roof (21) and floor (20). A goat isformed at (2), because the roof of the excavated portion of the panelcan no longer support the weight of the material thereabove. Angularmovement of the jet (22) cuts ore from the face (15) which then flowsdown the floor (20) to the face at (16) and thence along theintersection of the eroded face (14) and the floor (20) into the ditchin the roadway (not shown) and outward.

While it is not shown in this figure, the potential exists to not usethe jet (22) to cut the full way to the goaf (2) but rather leave anarrow pillar between, which is parallel to borehole (17). This pillarthen serves to control the failure of the roof (21) into the area whereflow of the mined ore slurry takes place. The use of such parallelpillars also retards goaf formation and permits ventilation of themining area.

FIG. 5 illustrates the drilling operation conducted up dip from roadway(10). The dip direction is marked by an arrow (18). Here, the roadway(5) is at a higher elevation than the roadway (10), but the mining withthe hydraulic jet starts at the higher end of the panel. The drill rigis positioned in the downhill roadway (10) at (31) and has drilled upgrade to position (32) in the roadway (5). The borehole (17) is thenreamed out and a lateral jetting bit (not shown) is attached to the endof the drill string (not shown). In the figure, the jetting bit is atlocation (16) and is shown cutting the face (15) of the ore panel. Themined ore and fluid flow down the borehole (17) to location (31) andthence into the ditch (not shown) in the roadway (10).

From the foregoing, it can be seen that ore panels can be mined withoutthe utilisation of heavy and expensive equipment which is difficult tomove from one panel to another. According to a feature of the invention,the mining of a panel of ore is commenced by forming a borehole from oneroadway on one side of the panel, to the opposite roadway on the otherside of the panel. The roadways are preferably sloped to carry the minedslurry of ore and a liquid used to erode the face of the panel.Similarly, the borehole is sloped so that the mined ore can be carriedas a slurry either in it or along its former position to the downhillroadway. Once the initial borehole is formed through the ore panel tothe opposite roadway, the drill bit is changed to a hydraulic jet, and apressurised liquid is used to erode the sidewall of the borehole as thehydraulic jet is withdrawn back down the borehole. The sweeping up anddown of the hydraulic jet as it is moves down the borehole forms a faceof the ore panel. Once the first pass of the hydraulic jet is made toerode the sidewall of the borehole and the orebody across the panel, asecond borehole is formed through the ore panel, and the hydraulic jetis again used to erode a subsequent slice of the panel face. The processcontinues until the entire panel of ore has been mined. During themining of the ore using the hydraulic jet, the ore and liquid form aslurry that is carried down the bottom of the mined area, and again downthe downhill roadway to a sump. A goaf is formed after an area has beenmined, as the mined area can no longer support the roof. Should the roofof the mine prematurely collapse, a new borehole can be formed and themining operation again commenced to continue mining the ore panel. Evenif the ore formation is not oriented on slope, which is optimum, themining operation can be carried out by forming the opposite gateroadswith different elevations so that the slurry of ore is neverthelesscarried downhill by the action of gravity. The system is best but notexclusively suited to narrow orebodies which are soft and thus easilyeroded while having a hard roof and floor which is not easily eroded andwhich does not cave near the face. Thus an open area is left adjacent tothe face and between it and the goaf to permit ventilation between thegateroads. The prudent use of the system would involve the capability toventilate the upper and lower gate roads independently in the event of aface collapse which blocks air flow between gateroads. The use of thesystem following gas drainage drilling could be advantageous as the gasdrainage boreholes could be re-used as the boreholes from which miningis undertaken by the described methods. Another advantage of the systemis that the maximum amount of mining hardware that is at risk is thedrill string, survey and surveillance tools and either a downhole motorand bit or the jetting assembly. This is significantly less machinerythan is involved in conventional longwall mining operations.

While the preferred and other embodiments of the invention have beendisclosed with reference to specific mining methods, structures andequipment, it is to be understood that many changes in detail may bemade as a matter of engineering choices without departing from thespirit and scope of the invention, as defined by the appended claims.

1. A method of mining ore from a formation, comprising: forming anunderground upper roadway and an underground lower roadway in saidformation to define an ore panel therebetween; forming said lowerroadway at an elevation generally below said upper roadway, and slopingthe lower roadway downhill; locating borehole drilling equipmentunderground in one of said upper roadway or said lower roadway; forminga sloping borehole with a drill string connected to said drillingequipment, said sloping borehole formed from one said roadway to theother roadway and through the ore panel to be mined, and moving thedrilling equipment in the roadway each time a different sloping boreholeis formed; using a jetting nozzle attached to the end of the drillstring to produce a high pressure jet of a liquid; moving the jettingnozzle through said borehole to erode the ore panel, where thepressurized liquid forms a slurry with the mined ore; and allowing theslurry of mined ore and liquid to flow down the lower roadway to a sump.2. The method of mining ore as described in claim 1, further includingforming a face in the ore panel by the erosion process, and forming afloor as the face of the ore panel recedes during the erosion process,and forming the floor with the solid panel of ore on one side, and agoaf on the other side.
 3. The method of mining ore as described inclaim 1, further including creating a series of enlarged holes fromwhence ore is removed, with pillars of the ore panel standingtherebetween.
 4. The method of mining as described in claim 1, furtherincluding sloping the upper and lower roadways and forming ditchestherein for the conveyance of the slurry of mined ore to the sump. 5.The method of mining as described in claim 1, further including drillingthe bore hole from the upper roadway through the ore panel to the lowerroadway; connecting the lateral jetting nozzle to the drill string atthe lower roadway; using the drill string to move the jetting nozzleuphill toward the upper roadway, and controllably rotate the jetting bitso that an enlarged hole or face is formed in the ore panel by the jetof high pressure liquid; and producing an ore bearing slurry by theerosion, and transporting the ore bearing slurry down the enlarged holeof the mining face created by the erosive process, to the lower roadway.6. The method of mining as described in claim 1, further includingdrilling the borehole from the lower roadway through the ore panel tothe upper roadway; attaching a reaming system to the drill string at theupper roadway; reaming the borehole to a larger diameter; attaching alateral jetting bit to the drill string; and using the jetting bit toerode the ore panel, starting at the upper level of the borehole, wherethe eroded ore then flows as a slurry back down the enlarged borehole tothe lower roadway.
 7. The method of mining as described in claim 1,further including using a directional bottom hole assembly attached tothe drill string to enable the drilling of a directionally controlledborehole in the ore panel.
 8. The method of mining as described in claim1, further including moving the jetting nozzle through the borehole toerode a sidewall thereof and form a face of the ore panel, and thencontinuing the movement of the jetting nozzle laterally across the faceof the ore panel to mine the ore of the formation.
 9. The method ofmining as described in claim 1, further including moving the drillstring into a different borehole to mine a new slice of the ore panel.10. The method of mining as described in claim 1, further includingforming a pillar adjacent to one said upper or lower roadway to protectthe roadway from collapsing, and forming said pillar by leaving thepanel intact at the location of the pillar.
 11. The method of mining asdescribed in claim 6, further including eroding a face in the ore panelto form a shape to induce backflow of the slurry toward the borehole tomine the ore panel.
 12. The method of mining as described in claim 6,further including forming the borehole at an angle with respect to ahorizontal reference so that the slurry is carried downhill by theborehole.
 13. The method of mining as described in claim 1, furtherincluding using the jetting nozzle that produces a narrow jet of highpressure liquid oriented generally in plane perpendicular to the drillstring so as to permit erosion of the ore panel.
 14. The method ofmining as described in claim 1, further including forming a goaf atlocations where the mined ore is removed from the ore panel.
 15. Themethod of mining as described in claim 2, further including mining theore panel by sweeping a high pressure liquid jet across the face of theore panel to mine the face of the ore panel and cause the ore panel faceto recede and form the sloping floor, and allow the ore bearing slurryto flow down the sloping floor along the solid ore panel of ore, awayfrom the goaf and toward the lower roadway.
 16. The method of mining asdescribed in claim 1, further including using a visual survey system ata mining location where the ore panel is eroded by the jetting nozzle toprovide a remote video representation of the operation.
 17. The methodof mining as described in claim 1, further including using an acousticor other survey system at a mining location where the ore panel iseroded by the jetting nozzle to provide a remote representation of theoperation.
 18. The method of mining as described in claim 1, furtherincluding using a survey system to provide an operator with knowledge ofthe orientation of the jetting nozzle.
 19. The method of mining ore asdescribe in claim 1, further including moving the drilling equipmentdownhill in one said upper or lower roadway each time mining of a sliceof an ore panel has been completed.
 20. The method of mining ore asdescribed in claim 1, further including forming a lateral roadwayperpendicular to both said upper roadway and said lower roadway, saidlateral roadway sloping downhill from said upper roadway to said lowerroadway so that a slurry of mined ore from an ore panel located abovesaid upper roadway can flow down said lateral roadway to said lowerroadway and then to said sump.
 21. The method of mining ore as describedin claim 1, further including sweeping the jetting nozzle about an arcfrom a floor of the formation to a roof of the formation, and moving thejetting nozzle axially along said borehole to cause a face of the orepanel to recede in the direction of movement of the jetting nozzle, andallowing the slurry to flow downhill on the floor toward the boreholeand then perpendicular downhill to the lower sloping roadway.
 22. Themethod of mining ore as described in claim 21, further including movingthe jetting nozzle downhill from one borehole to a subsequent boreholeto mine subsequent slices of said ore panel.
 23. A method of mining orefrom a formation, comprising: defining plural panels of ore to be minedin said formation; forming an underground upper roadway and anunderground lower roadway in said ore panel; forming said lower roadwayat an elevation lower than said upper roadway, and sloping said lowerroadway downhill; locating borehole drilling equipment underground inone of said roadways; forming a sequence of adjacent sloping boreholeswith a drill string and drill bit connected to said drilling equipmentfrom one roadway to the other roadway and through an area of the orepanel to be mined, and moving the drilling equipment in the roadway eachtime a sloping borehole is formed; using a jetting nozzle attached tothe end of the drill string to produce a high pressure jet of a liquid;moving the jetting nozzle axially through each borehole to erode a sliceof the ore panel between boreholes, and eroding the ore panel with thepressurized liquid to form a slurry of the mined ore, the eroding of theore panel forming a sloped junction where a face of the unmined orepanel joins a floor formed by the mined ore panel; and allowing theslurry of the mined ore and liquid to flow down the sloped junction tothe downhill sloping lower roadway, and then to a sump.